A Marine security detachment raises the U.S. flag at the dedication ceremony for the new U.S. Embassy in Baghdad, in 2009. (Sgt. 1st Class Derren Mazza / Marine Corps)

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The Senate voted Wednesday to authorize a 1,000 person increase in the size of the Marine Corps to provide additional protections for U.S. embassies and consulates, a direct response to the Sept. 11 attack on the a diplomatic facility in Benghazi, Libya, which resulted in the death of a U.S. ambassador and three other Americans.

The additional Marines would be assigned to the Marine Corps Embassy Security Group at Quantico, Va., and to regional commands and detachments at embassies, consulates and diplomatic facilities. The extra personnel would be authorized beginning Oct. 1, 2013, and would be available for three years.

It's not immediately clear how this would affect the Marine Corps' ongoing personnel drawdown. Current plans call for shedding about 5,000 Marines from active duty each year through 2016 as the service works toward a new authorized end strength of 182,100. Officials at Marine Corps headquarters could not immediately address the question.

Because there is no similar provision in the House version of the defense bill, the fate of this effort will be determined by negotiations involving the House, Senate, Defense Department and White House as they hash out final details of the measure. Those negotiations won't begin until the Senate passes its full version of the $648.5 billion bill, something not expected before Friday.

Sen. John McCain, R-Ariz., who offered the amendment, said the Benghazi attack was "a stark reminder that the security environment confronting American personnel serving in U.S. embassies and consulates abroad is as dangerous as any time that I can remember."

The additional 1,000 Marines are needed, he said, because there are many diplomatic facilities that have no Marine Corps personnel providing security and many facilities that have Marine security guard detachments of only six people.

"Today, there are 126 U.S. diplomatic missions outside the United States without Marine Corps security protecting [them], including parts of Asia and Africa where we suspect that al Qaida is expanding its presence," McCain said.

Extra Marines are needed, he said, because moving Marines from some diplomatic facilities to improve security at other facilities would be unwise. "Increasing one — as is necessary in light of the attack at Benghazi — cannot come at the expense of another," he added.

In addition to the extra Marines, the amendment calls for a reassessment by the Defense Department of the risk for diplomatic personnel. That does not necessarily mean a detachment is needed at every diplomatic facility, McCain said.

The Benghazi attack killed the U.S. Ambassador to Libya, J. Christopher Stevens, Foreign Service Officer Sean Smith and security officers Tyrone S. Woods and Glen A. Doherty. The incident has been heavily scrutinized, and numerous questions have been raised — on Capitol Hill and beyond — once it became clear there was no Marine Corps presence at the compound.

Marine Security Guard detachments are deployed based on requests made by the State Department. An official there told Marine Corps Times last month that an independent review board was convened to examine the Benghazi assault and make recommendations for improving security at its facilities.

The Embassy Security Group is expected to add detachments over the next five to 10 years, but Marine officials insist that growth effort has been in place since 2004 — and that it's not a knee-jerk response to recent events. They have, however, declined to say what the group's projected size will be when that growth is complete.

Currently, more than 1,200 Marine security guards are assigned to more than 130 countries. Their training program lasts seven weeks, and the Marine Security Guard School can accommodate 200 students per class.

The schoolhouse at Quantico is only for those assigned to Marine security guard duty, but the Embassy Security Group provides training to other units and government agencies, including the FBI and State Department.

Additionally, the Embassy Security Group intends to expand training opportunities for the Marine Corps' Fleet Antiterrorism Security Teams, officials have said. FAST platoons can be called in to shore up embassy security, as they were in the aftermath of the attack in Libya and another in Yemen.